Sky's Charlotte Hawkins outlines what's at stake for the candidates on the biggest day in the run-up to the US presidential elections.

The states are up for grabs today, count for just half of the delegates at the party conventions in the late summer. Now in the democrat race six states have officially voted already and it's a straight fight between Barrack Obama and Hillary Clinton. Obama took first blast, winning the Iowa caucuses in early January but then Mrs Clinton struck back with an unexpected victory in New Hampshire. Since then Clinton won in Nevada and Obama took south Carolina. Michigan and Florida's primaries don't count because of a dispute over how they brought their elections forward. So the democratic rivals are equal when it comes to states, but Hillary Clinton is ahead on the number of delegates. As of tonight, she has two hundred and sixty one to Barrack Obama's a hundred ninety. The winner needs two thousand and twenty five to win the party's nomination.

Now in the race to become the republican nominee, eight states have voted. Mik, Mike Huckabee got off to a flying start by taking Iowa. Then John Maccain won in New Hampshire, Mitt Romney took Wyoming, Michigan and Nevada before John Maccain won in South Carolina. Last week, he also took Florida but Romney won again at the weekend in Maine. The Florida win put John Maccain ahead in the delegate race. He has ninety-three to Mitt Romney's seventy-seven. Mike Huchabee has forty. The winning republican candidate will need the backing of one thousand one hundred and ninety one delegates to win the nomination. So it 's all to play for as we are going to Super Tuesday.

WORDS IN THE NEWS

1. up for grabs : phrasal

If something is up for grabs, it is available to anyone who is interested. (INFORMAL)

2. caucus : n-count

A caucus is a group of people within an organization who share similar aims and interests or who have a lot of influence. (FORMAL)

3. strike back : phrase

If you strike back, you harm or criticize someone who has harmed or criticized you.

4. get off to a flying start : phrase

If someone or something gets off to a flying start, or makes a flying start, they start very well, for example in a race or a new job.